It is well known to use catalysts containing a rare earth element for polymerization of a conjugated diene. Polymerization of butadiene by use of rare earth complexes such as neodymium naphthenate has been reported in the "Journal Polymer Science", Vol. 18, 3345 (1980). However, other work in this area is disclosed in U.S. Pat. Nos. 4,242,232 to Sylvester et al, 4,696,984 to Carbonaro et al, and 5,360,898 to Jordaan et al, displaying that neodymium naphthenate can be very difficult to dissolve in a hydrocarbon solvent and produces a gel. Such gels require the use of a relatively large amount of quantities of various viscosity reducing additives, generally in an amount exceeding two moles of additive per each mole of rare earth complex. In said literature reference, polymerization of butadiene is displayed using a ternary catalyst consisting of NdCl.sub.3, an alcohol and Al(C.sub.2 H.sub.5).sub.3. However, when a catalyst system consisting of this combination is used for polymerization many problems arise because NdCl.sub.3 is solid and insoluble in a hydrocarbon solvent and the resulting catalyst component is heterogeneous. Heterogeneous catalysts are disadvantageous for use in industrial operations. Furthermore, catalyst systems consisting of the combination described above have defects, for example, low polymerization activity.
Additionally, such catalysts when treated with viscosity reducing additives are disadvantageous for industrial use for a variety of other reasons. For example, the use of ethers can reduce the stereospecificity of the catalyst. The use of trialkylaluminum compounds can cause the molecular weight distribution to broaden and its molecular weight to decrease. The use of protic viscosity reducing agents can result in the need for more cocatalyst in some polymerizations, thereby raising the cost of catalyst. Finally, the introduction of certain types of viscosity reducing additives can complicate other types of polymerizations if the additives become incorporated into the facilities solvent stream.
The object of this invention is to overcome these disadvantages and to eliminate or reduce the high viscosities occurring upon the mixture of a rare earth complex in a hydrocarbon solvent.